Stoker



July lo, 1945. 1 M P|| CHER ET AL 2,380,260

STOKER Filed April 1'9,l 1944 :immun v 634m, Joa@ me Arrowe Ys.

Patented July 10, 1945 STOKER John Mason Pilcher, State College, andFrank F.

Dennis, Philadelphia, Pa., assgnors to Pennsyl- Vania, Bituminous CoalResearch, Inc., Altoona, Pa., a corporation of Pennsylvania ApplicationApril 19, 1944, Serial No. 531,824

` (o1. rio-45) 7 Claims.

This invention relates to stokers, more particularlyl,` to underfeedstokers which operate on the prinf'ciple of partial oxidation of coalprior to its undergoing active combustion.

Underfeed stokers as ordinarily constructed do not operatesatisfactorily with strongly coking coals, such as the Pennsylvaniacoking coals. That is, when it is attempted to burn a strongly cokingcoal in an underfeed stoker of customaryl sivecas actually to extinguishthe fire or to push open the furnace door.

A method of and apparatus for avoiding the formation of coke trees fromcoking coals by mild- .ly oxidizing .the coal before active combustionbegins are described and claimed in an applica- `.tion filed by'I'heodore S. Spicer and Calvert C.

Wright on April 15, 1941, Serial No. 388,626. More in detail, as thecoal moves upwardly into and through the'lower end of the retort ofthestoker it is heated by conduction of heat downwardly from the activelyburning coal and in that portion of the column of coal in which the coalis heated but is not yet plastic, i. e., where coking has not begun, thecoal is oxidized to an extent such as to reduce but not destroy itscoking power. This oxidation is chiefly a surface phenomenon but doesnot involve active combustion. 'Ihis is accomplished by introducingan-oxidizing agent, most suitably air or yan air-stream mixture, intothe coal at a point or in a region such that it comes into intimatecontact with the heated but non-plastic coal. vFor brevity thisprocedure is referred to as a preoxidation method of operating astoker,` or as the preoxidation principle.

Extended experience has demonstrated-amply that the preoxidation methodeasily and satisf factorily represses coke tree formation providedcertain critical .details are observed. In the rst place, the coal mustbe mixed intimately with the oxidizing agent as it .moves upwardlythrough the' preoxidation zone'. Second, as the coal is mixed andelevatedl any substantial segregation must be avoided, i. e., it isnecessary to maintain substantial uniformity of coal size distributionacross the section while mixing all of the coal intimately with theoxidizing agent. These features result in subjecting all of the coaluniformly to the action of the preoxidizing air or other oxidizing agentbut observance of them is necessary because it has been found that coketree suppression is not attained satisfactorily if the coal is notthoroughly mixed with the air or if the air distribution is not uniformdue to channeling or segregation of the coal into regions containinglargely fines and regions containing largely coarse particles. And asindicated above, the coal must be heated but not sumciently to render itplastic,

continuously unobstructed opening for rotation' and enough oxidizingagent must be supplied to produce the desired oxidationbefore coking ofthe coal begins.

Although the necessary elevation and mixing of the coal withoutsegregation in the preoxidation zone may be accomplished satisfactorilyin various ways, the simplest and most eective means for doing sois avertical screw; Likewise, although the oxidizing agent might beintroduced into the coal at any point prior to the preoxidation zone, itis preferred to supply the oxidizing agent through a supplementary, orpreoxidi'zing tuyre situated below the regular or active combustiontuyres at a distance such that thb agent enters the coal substantiallyat the lower end of the preoxidation zone.

It has been found in actual practice that in the operation of such astoker there is a tendency for coal to enter the supplementary tuyre,even to the extent of closing the tuyre opening. This is serious becauseit decreases the amount of air supplied by the supplementary tuyre tothe coal and coke trees result because the coal is not oxidizedsufficiently. Moreover, continued operation may completely ll the tuyrevopenings and by forcing coal through the supplementary tuyre cause thewind box to be filled with riddlings, which is objectionable.

Means for alleviating the problem of riddlings in the supplementarytuyre are disclosed and claimed in a copending application, Serial No.509,071, filed November 5, 1943, by Speer W.

Guthrie, now PatentNo, 2,366,783, dated January 9, 1945. In accordancewith that invention the supplementary vtuyre is constructed to have atherein of a scraper member which acts to clear coal riddlin'gs fromthev opening. vThe embodiment shown includes a vertical screw as thepre--` the edge of the screw flight at a level such that it movesthrough, or around, the tuyre opening when the screw is rotating duringthe on periods of the stoker.

As far as we are aware, the construction shown 5 opening of thesupplementary tuyre and thus permits the tuyre to perform its intendedfunction efficiently. However, while it keeps the tuyre open it tends topush some riddlings into the wind box. While not an insuperable;obstacle,

that tendency is undesirable because it necessitates periodic cleaningof the wind box and, particularly with domestic stokers, stoker buildersseek to eliminate such upkeep requirements. as far as possible. -f

A scraper connected to the edge of the'screw 20 flight likewise acts atthe same time and in the same plane that the horizontal component of theelevating action of the screw is at a maximum, whereas it would bedesirable for the scraper action to lag that component in the plane ofthe tuyre opening. A construction which accomplishes that is disclosedand claimed in another copending application, Serial No. 509,651, filedNovember l0,- 1943, by Calvert C. Wright, now

Patent No. 2,362,604, dated November 14, 1944.

the preoxidation tuyre leads the scraper, suitably by about one-fourthturn of the screw, and preferably the scraper is connected to the shaftclosely adjacent the underside of the flight. This construction performsmore eiciently than the reference to the accompanying drawing in whichFig. 1 is a vertical sectional view through the significant part of apreoxidation type Stoker constructed in accordance with one embodimentof the present invention; Fig. 2 a horizontal section taken on lineII-II, Fig. 1; Fig. 3 a plan.

view of the preferred type of scraper; and Fig. 4 a perspective view ofone of the scraper blades shown in Fig. 3. y

The present invention is predicated upon our discovery that theoperationof scrapers mounted v in accordance with the principle of the aforesaidapplication of Calvertl C. Wright is improved, While retaining theadvantages of that invention, by mounting them for freedom of movementupwardly and downwardly in and laterally of the preoxidation tuyre. Inthat way binding and related interference due to lodgment of large pie sof coal is avoided.

A urther important feature of the invention is the provision of ascraper whose leading edge is designed so that the thrust exerted by itis directed substantially entirely inwardly, i. e., toward the retort,whereby there is no tendency for the scraper to push coal into the windbox.

Through combining both of these features we satisfactorily accomplishcleaning of the supplementary tuyre so that there is no interferencewith preoxidation to avoid coke tree formation.

Having reference now to Figs. 1 and 2, there is i shown a preoxidationtype of stoker comprising a retort I of conventional form provided withone or more main combustion tuyres which form the active combustion zonein the manner customary in the art. In the embodiment shown there aretwo such tuyres, 2 and 3, Fig. 1. The retort is surrounded by a windbox! supplied with air or other oxidizing agent from a main air duct '5in any suitable manner, as by a motor driven blower.

embodiment shown in the aforesaid application 40 Coal is ntrOduced t0the retort by a hOIZOntal of S. W. Guthrie, but it, too, is open todrawbacks. Thus, the scraper is rigidly connected to the screw shaft andbinding of the scraper may occur` because of its inflexibility when itencoun ters a firmly lodged piece of coal, or if a substantial amount ofriddlings piles up and packs forwardly of the scraper. Likewise, theclaw-like form of the leading edge of the scraper blade tends to pushsome portion of the riddlings into the wind box, as described above.

The major object of the present invention is to providea preoxidationtype stoker with simple, inexpensive and reliable means forautomatically keeping the supplementary, or preoxidation,

tuyre free from riddlings, and which not only does so more effectivelythan the means proposed heretofore, but also eliminates the tendency ofthose means to push a portion of the riddlings into the wind box. y

A further object is to provide a scraper for which is so constructedthat coal contacting it in the retort, immediately inside of the tuyre,passes easily over the blade instead of being pushed ahead.

Still another object is to provide a scraper of the foregoing type andfor attainment of the foregoing objects which effectively avoids pushingof riddlings into the wind box.

Other objects will appear from the following description.,

The invention will be described in detail with 76 such drive means formno part of this invention and because theyA are well understood in theart they do not require illustration or further description. l

Coal is delivered by screw conveyor 6 to the bottom of the retort whereit is picked up and moved upwardly by a Vertical screw ight 8 mounted ona vertical shaft 8a operated by a gear 9 and a pinion I0 which maysuitably be driven by the motor which operates screw 6. During the onperiods of the Stoker screw conveyor 8 moves the coal progressively andcontinuously` upwardly through the"r retort into the active combustionzone and in so doing the coal is mixed without segregation of particlesor pieces of varying sizes.

Disposed in wind box 4 is a partition I I which divides it into an upperair chamber I2 through which air is supplied to the main combustiontuyres 2 and 3, and a lower air chamber I3 through which air is suppliedto the preoxidation tuyre I4. Chambers I2 and I3 act as conduits forsupplying air to the main and supplementary tuyres, respectively.Mounted at the juncture of wind box 4 and the main air duct for pivotalmovement about the end of partition II is a butterfly valve I5. Bymoving it appropriately, as indicated by the broken line positions, Fig.1, the air supplied through duct 5 may -be apportioned in any desiredmanner between the upper and lower air chambers I2 and I3. Thus, all ofthe air may be passed to the upper tuyres 2 and 3, or all of it may bepassed to the preoxidation tuyre I4. In ordinary practice, however,valve l will be adjusted to supply an amount of air to tuyre I4 whicheffects preoxidation sufficient to prevent coke tree formation, and airnecessary for combustion is passed directly to the 'active combustionzone through upper air chamber l2 and tuyres 2 and 3. A smoke backopening I6 may be provided 'as shown' in Fig. l for the usual purpose ofpreventing back pressure at this point. The upper, or active combustion,tuyres 2 and 3 are, as will be observed from Fig.v l, of the usualsectional construction which forms a series of spaced openingsy betweenIwebs 2a and 3a. The preoxidation tuyre I4 has, however, a conltinuouslyunobstructed opening, as shown in the drawing, to permit a scrapermember il to enter and to pass completely around the tuyre opening tosweep from it any pieces of coal that may find their way into it.

In accordance with an important feature of the invention, the scraper Ilis carried by shaft 8a for movement laterally of and vertically in thetuyre M. To this end the arm I8 which carries the scraper is mountedloosely inthe shaft in such manner that the scraper is free to tiltupwafdly and downwardly, preferably over a total distance not greaterthan the height of opening I4, and so that it Vmay move inwardly andoutwardly with respect to the opening, this lateral movement beingrestricted so that at least `to the Scrapers, the sides Ma of tuyre [Ilacting as stops to prevent further movement in one direction While aportion of the opposite scraper I vreinains in the tuyre.

The curvature of the leading edges of the scraper ll shown in Fig. 2 issuch that the thrust is preponderantly toward the retort. Howeverg `thethrust at the heel of the blade mayl act to ,push coal in the retortahead of the scraper and through the tuyre into the Awind box. For thatreason. wejprefer to use scraper blades whose thrust is wholly inwardtoward the retort. This is accomplished, according to the invention, byso s aping the leading edge, or by so relating it from riddlings.

to the supportingarm, that as theV shaft 8a' rotates the thrust at allpoints of the blade edge will be toward the retort. Preferably this'isdone by making the leading edge of the blades Ila straight, instead ofcurved, and disposing it at an angle relative to the supporting arm Isa,as

shown inA Fig. 3, in which the arrows from the' the blade-that normallymoves in the retort up wardly and backwardly from the base ,of the ingin that /Way.

leading edge.,This isillustrated in Figs. 3 "and .4. The scraper bladeIla shown comprises a body having a heel lportion I 3 vfor connecting itto arm I8, and the straight leading edge 20 extends from the heel to thetip. This leading edge is, in accordance with preferred practicestraight and disposed angularly with respect to the heel so that all ofits thrust is inward. A portion of the leading edge adjacent the heel isbeveled upwardly and rearwardly from the base as shown at 2i to act as aramp to allow coalpulled or swept from the tuyre to ride up over andfall behind the bladeinsteadvof being pushed ahead of it.

The operation of a stoker constructed in ac.-v

cordance with the drawing will be understood is sufficient foriiitiation'fof 'the desired preoxidation but -insuicient to make itplastic. I Under the combined mixing action of conveyor 8, withavoidance of segregation. of nes, and of the'air introduced throughtuyre It, the coal is sumcently oxidized bythe time it reaches theplastic Zone, which lies atv or immediatelyabove Vthe upper end ofconveyor 8, that coke trees do not form when the coal burns in theactive combustion zone, i. e., in the region of tuyres 2 and 3. 1 Fromywhat has`been said it willbe .understood, it is believed,yhow the`scraper operates.I I f coal accumulates in the tuyre lll to such anextent that it cannot be dislodged easily, the scraper automaticallyvadjusts itself to take smaller bites and progressively clears the open-With the yspecial contouring of the scraper blade the wind box is keptfree Hence the preoxidation tuyre acts to perform the desiredpreoxidation without interference, or interruption, and the stokeroperates without coke tree formation.

The scraper'supporting arm I3 is most suitably carried by the screwshaft according L.t0 the preferred embodiment described in theaforesaidI application of Calvert C. Wright. That is, the

bore which receives the' arm is located not vfar lbelow the flight andat an angular position relaof the tuyre leads the scraper, suitably byabout one-fourth turn of the flight. In that case it is preferred tooperate the screw so that an open area occurs just above and belowv thescraper arm.

Various modifications are, of course, permissible. For example, thescrapell vmember may be connected in other `ways than shown in thedrawing, 'and other variations not departing from the gist of theinvention will occur to those skilled in the art.

This 4application together with all of the other applications referredto hereinabove are owned by a common assignee.

According to the provisions of the patent statutes, we have explainedthe construction and mode of Operationof our invention andhave il-'r'epresent its best embodiment.

lustrated and described what 'we now consider to desire to have itunderstood that, within thesscope However, We

, screw being disposed below the plane of said tuyre, a supplementarycontinuously unobstructed tuyre disposed in the retort wall below saidmain combustion tuyre for supplying an oxidizing agent to the coalengaged by said screw in a regionwhere the coal is heated but notplastic,

conduits for supplying an oxidizing agent to the l said tuyres, and ascraper member extending into said supplementary tuyre and looselycarried by the shaft of said screw Afor movement relative to said tuyreopening.

v 2. An underfeed stoker comprising thecombi-A nation of a substantiallyvertical retort provided with a main combustion tuyre at the upper portion Iwhere active combustion occurs, means for supplying coal to thelower end of said retort, a vertical screw disposed in said retort formoving coal upwardly in the retort, the upper end of said screw beingdisposed below the plane of said tuyre, a supplementary continuouslyunobstructed tuyre disposed in the retort wall below said maincombustion tuyre fo`supplying an oxidizing agent to `the coal engaged bysaid vertical screw in a region where the coal is heated but notplastic, conduits for supplying said oxidizing agent to the said tuyres,an arm mounted loosely in a bore through the shaft of said screw andextending from both sides of the shaft, and scraper members connected tothe ends of said arm and extending into said supplementary tuyre forkeeping it clear of coal.

3. An underfeed stoker comprising the combination of a substantiallyvertical retort provided with a main combustion tuyre at the upperportion where active combustion occurs; means for supplying coal to thelower end of said retort, a vertical screw disposedin saidv retort formoving coal upwardly in the retort, the upper end of said screw beingdisposed below the plane of said tuyre, a supplementary continuouslyunobstructed tuyre disposed in the retort wall below said maincombustion tuyre for supplying air to the coal engaged by said verticalscrew in a region where the coal is heated but not plastic, conduits forsupplying air to the said ,tuyres, and a scraper member extending fromwithin the retort into said `supplementary tuyre and loosely mounted ina bore through the shaft of said screw, the portion of said scraperwithin the 'retort being bev eled upwardly and rearwardly from the baseof its leading edge.

4. A stoker according to claim 1, said scraper member having a bodyportion terminating at one end in a heel and having a straight leadingedge disposed at a`n angle to said heel providing scraping thrust in thetuyre opening at said edge sub' stantially wholly inwardly from thetuyre opening toward the retort. l

5. A stoker according to claim 2, said scraper member having a bodyportion terminating at one end in a heel and having a straight leadingedge disposed at an angle to said heel providing scraping thrust in thetuyre opening at said edge substantially wholly inwardly from the tuyreopening toward the retort.

6. A scraper blade for rotation in a tuyre of a stoker to scrape solidmatter from the tuyre into the retort of the Stoker, saidblade having abody terminating at one end in a heel portion and having a straightleading edge extending along one side at an angle to the heel providingscraping thrust at said edge directed substantially wholly inwardly fromthe tuyre toward the retort.

7. A scraper blade for rotation in a tuyre of a stoker to scrape solidmatter from the tuyre into the retort of the stoker, said blade having abody vportion integral with a heel portion for connection'to a drivingmember and having a straight leading edge extending along one side at anangle to the heel providing scraping thrust at said edge substantiallywholly inwardly from the tuyre toward the retort, and said edge having aportion beveled rearwardly and upwardly from its base.

JOHN MASON PILCHER..Y FRANK F. DENNIS.

